<p>This term was used earlier in the national lighting standards. It was defined as the average illuminance in a furnished room with the lighting plant having completed half of its life cycle. For the new value (initial value) the nominal illuminance factor had been multiplied with the planning factor of 1.25. Today, the decrease in light intensity due to aging and pollution of the lamps, luminaires and the walls and ceilings in the room is taken into account with the maintenance factor. The values given in DIN EN standards for illumination are maintenance values.</p>